TakeN.h

#pragma once
 
#include <utility>
 
#include "../Common.h"
 
namespace CXXIter {
 
    // ################################################################################################
    // TAKE WHILE
    // ################################################################################################
    namespace op {
        template<typename TChainInput>
        class [[nodiscard(CXXITER_CHAINER_NODISCARD_WARNING)]] TakeN : public IterApi<TakeN<TChainInput>> {
            friend struct trait::Iterator<TakeN<TChainInput>>;
        private:
            TChainInput input;
            size_t n;
            size_t remaining;
        public:
            constexpr TakeN(TChainInput&& input, size_t n) : input(std::move(input)), n(n), remaining(n) {}
        };
    }
    // ------------------------------------------------------------------------------------------------
    template<typename TChainInput>
    struct trait::Iterator<op::TakeN<TChainInput>> {
        using ChainInputIterator = trait::Iterator<TChainInput>;
        using InputItem = typename TChainInput::Item;
        // CXXIter Interface
        using Self = op::TakeN<TChainInput>;
        using Item = InputItem;
 
        static constexpr inline IterValue<Item> next(Self& self) {
            if(self.remaining == 0) [[unlikely]] { return {}; }
            auto item = ChainInputIterator::next(self.input);
            if(!item.has_value()) [[unlikely]] { return {}; }
            self.remaining -= 1;
            return item;
        }
        static constexpr inline SizeHint sizeHint(const Self& self) {
            SizeHint input = ChainInputIterator::sizeHint(self.input);
            return SizeHint(
                std::min(input.lowerBound, self.n),
                SizeHint::upperBoundMin(input.upperBound, self.n)
            );
        }
        static constexpr inline size_t advanceBy(Self& self, size_t n) {
            size_t skipN = ChainInputIterator::advanceby(self.input, n);
            if(self.n < skipN) { self.n = 0; } else { self.n -= skipN; }
            return skipN;
        }
    };
    template<CXXIterExactSizeIterator TChainInput>
    struct trait::ExactSizeIterator<op::TakeN<TChainInput>> {
        static constexpr inline size_t size(const op::TakeN<TChainInput>& self) {
            return trait::Iterator<op::TakeN<TChainInput>>::sizeHint(self).lowerBound;
        }
    };
}